Since you said this coworker acts cold toward you even when you're in a good mood, I wanted to point out something else about negative people, or bullies, in the workplace. Your being in a good mood may actually set your coworker off.

After my job started getting easier on me physically and I felt better, I began being more upbeat. At first, I pretended to be cheerful just to be sarcastic, but when I began having fun with it I found I actually did feel happier despite my whole work situation. I also found that being cheerful actually annoyed the bullies. They are miserable people who want to make other people's lives miserable, too. But, other coworkers enjoyed my upbeat attitude so it rubbed off on them.

Try to keep a smile on your face no matter what. It might annoy those who are miserable people in the first place, but might bring sunshine to someone else's life. Here is a quote I found which I made my mantra while on that job: